1. Technical Field of the Invention
The present invention relates to an electrophoretic device using an electrophoretic phenomenon, a method of manufacturing the electrophoretic device, an electronic apparatus, a microcapsule, and a method of manufacturing the microcapsule.
2. Discussion
An electrophoretic phenomenon generally uses an electric double layer produced in an interface between a solid (charged particle) and a liquid (dispersion medium), and represents a phenomenon in which a charged particle migrates to an electrode having polarity opposite to the charge possessed by the charged particle by using, as motive power, the force exerted by an electric field.
An electrophoretic display (EPD) using such a phenomenon has a simple structure, a wide viewing angle, a high contrast ratio, a low driving voltage, low power consumption and the ability to hold a display image (referred to as a “memory effect” hereinafter), and attracts attention as a display having various characteristics which cannot be easily realized by a CRT (Cathode Ray Tube) display and a liquid crystal display.
The electrophoretic display comprises a pair of substrates, and an electrophoretic dispersion liquid which is sealed between the substrates with partitions provided therebetween, and which comprises charged particles basically positively or negatively charged, and a liquid dispersion medium having an insulating property, an electrode being formed on the inner side of each of the substrates. In this display, when a voltage is applied between the substrates, the charged particles migrate to the electrode having polarity opposite to the charge possessed by the charged particles. In this case, the charged particles and the dispersion medium are colored in different colors to permit a display on one of the substrate sides.
Namely, when the charged particles move to one of the substrates, which serves as a display surface, the color possessed by the charged particles is recognized, while when the charged particles move to the other substrate, the color of the dispersion medium is recognized.
In the electrophoretic display, charge is held by the electrodes when a circuit is opened immediately after a voltage is applied, and thus the charged particles can be adsorbed by the Coulomb's force of the charge held by the electrodes. Namely, a certain still image can continuously be displayed with no voltage applied.
However, the long-term use of the electrophoretic display having the above construction causes a problem in which adhesion of the charged particles to the electrodes proceeds to deteriorate display response and contrast.
In order to solve this problem, Japanese Unexamined Patent Application Publication No. 59-1719431 discloses means for forming a polyimide thin film having a thickness of 5 nm or less on the surface of an electrode. Also, Japanese Unexamined Patent Application Publication No. 01-248182 discloses means for forming a fluorocarbon resin thin film on the surface of an electrode.
These adhesion preventing means cause a repulsive force between the hydrophobic surface of the electrode and the hydrophilic surfaces of the charged particles to suppress adhesion of the charged particles to the electrode, thereby improving display response and permitting long-term maintenance of good contrast.
Another known example of the construction of the electrophoretic display is a microcapsule-type electrophoretic display in which an electrophoretic dispersion liquid comprising charged particles and a dispersion medium is enclosed in a plurality of microcapsules, and the microcapsules are held between a pair of substrates.
However, in the microcapsule-type electrophoretic display, the microcapsules are present between an electrode and the charged particles, and it is thus difficult to use the above-described adhesion preventing means.
The present invention has been achieved in consideration of the above-described conditions, and an object of the present invention is to provide an electrophoretic device capable of realizing an improvement in display response and long-term maintenance of good contrast, a method of manufacturing an electrophoretic device, an electronic apparatus, a microcapsule, and a method of manufacturing a microcapsule.